Telescopic shaft for motor vehicle steering

ABSTRACT

A telescopic shaft for motor vehicle steering assembled in a steering shaft of a motor vehicle and constructed by non-rotatably and slidably fitting a male shaft and a female shaft has a first torque transmission member and a second torque transmission member. The first torque transmission member is interposed, with an elastic body in between, between axial grooves formed in one line in an outer peripheral surface of the male shaft and an inner peripheral surface of the female shaft, respectively. The second torque transmission member is interposed between axial grooves formed in the other one line in the outer peripheral surface of the male shaft and in the inner peripheral surface of the female shaft, respectively. The elastic body has transmission member-side contact portions in contact with the first torque transmission member, groove surface-side contact portions separated in the circumferential direction with predetermined intervals and in contact with groove surfaces of the axial groove of the male shaft or the female shaft, and an urging portion for elastically urging a transmission member-side contact portion and a groove surface-side contact portion in the direction to separate them from each other. Rigidity of the transmission member-side contact portion and that of the groove surface-side contact portions are made different from each other.

TECHNICAL FIELD

The present invention relates to a telescopic (extensible/retractable)shaft for a vehicle steering, assembled in a steering shaft of a vehicleand constructed by fitting a male shaft and a female shaft to each otherso as to be unable to rotate but to be slidable.

BACKGROUND ART

What is required of a telescopic shaft of a steering mechanism unit ofan automobile is performance of absorbing an axis-directionaldisplacement occurred when the automobile travels, and not transferringthe displacement and vibrations onto a steering wheel. Further, anotherrequirement is a function of shifting a position of the steering wheelin an axis-direction and adjusting this position in order for a driverto obtain a position optimal to driving a car.

In all these cases, the telescopic shaft is required to reduce backlashor rattling noises, a feeling of the backlash on the steering wheel andslide resistance occurred when performing a sliding operation in theaxis-direction.

Such being the case, a conventional contrivance is that metallic noises,metal butting noises, etc are absorbed or reduced by coating a maleshaft of the telescopic shaft with a nylon film and applying grease overa slide portion, and the slide resistance and the backlash in a rotatingdirection are thus reduced.

There is, however, a case where abrasion of the nylon film progresses inthe course of its being used, and the backlash in the rotating directionincreases. Further, under such a condition as to be exposed to a hightemperature in an engine room, the nylon film suffers a volumetricchange with the result that the slide resistance conspicuously rises andthe abrasion is highly accelerated, wherein the backlash in the rotatingdirection increases.

Under such circumstances, according to telescopic shafts disclosed inGerman Patent Publication DE3730393C2, Japanese Patent ApplicationLaid-Open No.2001-50293 and Japanese Patent Application Laid-OpenNo.2001-193738, a rolling member and an preload elastic member forpreloading a male shaft and a female shaft, are interposed between anouter peripheral surface of the male shaft and an inner peripheralsurface of the female shaft. With this configuration, when sliding, theelastic member preloads the rolling member against the female shaft etcto such an extent as not to cause the backlash, whereby the backlashbetween the male shaft and the female shaft can be prevented. Further,when transferring the torque, the elastic member can restrict therolling member in a peripheral direction, and the male shaft and thefemale shaft can prevent their backlashes in the rotating directionthereof.

According to all these Patent documents, however, the elastic member forpreloading the rolling member and a race portion abutting on the rollingmember are made from different materials and take different shapes fortheir usage.

The reason why so is that the race portion abutting on the rollingmember must bear a high contact surface pressure. This implies that thetorque must be transferred via the rolling member, and hence the raceportion abutting on the rolling member is required to be a hard andrigid member. By contrast, the elastic member for generating a biasingforce, it is required to be made from a flexible material as in the caseof a spring.

From these points described above, according to the Patent document,i.e., German Patent Publication DE3730393C2, the race portion abuttingon the rolling member involves using a different material and adifferent shape, and, as a result, it follows that a rise inmanufacturing cost is brought about.

Moreover, German Patent Publication DE3730393C2 exemplifies an exampleof a plate spring, wherein the race portion and the elastic member aremade from a single material. However, the plate springs are connectedvia a web, so that the configuration becomes complicated, resulting in arise in assembling cost. Further, as described above, for transferringthe torque through the rolling member, the plate spring has a difficultyin terms of utilization to make it compatible to bear the contactsurface pressure of the rolling member and to give the basing force.

Furthermore, Japanese Patent Application Laid-Open No.2001-193738exemplifies an example, wherein the elastic member and the race portionare integrally formed. As in the case described above, however, fortransferring the torque via the rolling member, the plate spring has thedifficulty in terms of utilization to make it compatible to bear thecontact surface pressure of the rolling member and to give the biasingforce.

DISCLOSURE OF THE INVENTION

It is an object of the present invention, which was devised in view ofthe circumstances described above, to provide a telescopic shaft for avehicle steering that is capable of actualizing a stable slide load andtransferring a torque in a high-rigidity state.

To accomplish the above object, according to the present invention, atelescopic shaft for a vehicle steering, assembled in a steering shaftof a vehicle and constructed by fitting a male shaft and a female shaftto each other so as to be unable to rotate but to be slidable, thetelescopic shaft comprising:

a first torque transferring member interposed via an elastic memberbetween one line of axis-directional groove and one line ofaxis-directional groove formed respectively on an outer peripheralsurface of the male shaft and on an inner peripheral surface of thefemale shaft; and

a second torque transferring member interposed between another line ofaxis-directional groove and another line of axis-directional grooveformed respectively on the outer peripheral surface of the male shaftand on the inner peripheral surface of the female shaft,

the elastic member including:

a transferring member sided contact portion abutting on the first torquetransferring member;

a groove sided contact portion spaced away at an predetermined intervalsubstantially in a peripheral direction from the transferring membersided contact portion and abutting on a groove surface of theaxis-directional groove of the male shaft or the female shaft; and

a biasing portion elastically biasing the transferring member sidedcontact portion and the groove sided contact portion in such a directionas to separate from each other,

-   -   wherein a rigidity of the transferring member sided contact        portion is differentiated from a rigidity of the groove sided        contact portion.

Further, in the telescopic shaft for the vehicle steering according tothe present invention, it is preferable that the first torquetransferring member is a rolling member rolling when both of the maleshaft and the female shaft make relative movements in theaxis-direction, and

-   -   the second torque transferring member is a slide member sliding        when both of the male shaft and the female shaft make the        relative movements in the axis-direction.

Moreover, in the telescopic shaft for the vehicle steering according tothe present invention, the biasing portion of the elastic member cantake a bent shape bent between the transferring member sided contactportion and the groove surface sided contact portion.

Further, in the telescopic shaft for the vehicle steering according tothe present invention, the elastic member can be constructed of anintegral molding product made from thin plate spring steel.

Still further, in the telescopic shaft for the vehicle steeringaccording to present invention, surface hardness of the transferringmember sided contact portion can be set higher than surface hardness ofa portion extending from the groove surface sided contact portion to thebiasing portion.

Yet further, in the telescopic shaft for a vehicle steering according tothe present invention, the biasing portion can be formed with holes forreducing a biasing force.

Moreover, in the telescopic shaft for the vehicle steering according tothe present invention, a plate thickness of the transferring membersided contact portion can be set thicker than a plate thickness of aportion extending from the groove surface sided contact portion to thebiasing portion.

Still moreover, in the telescopic shaft for the vehicle steeringaccording to the present invention, the transferring member sidedcontact portion can be formed substantially in a circular arch shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a steering mechanism unit of an automobile, towhich a telescopic shaft for a vehicle steering according to anembodiment of the present invention is applied;

FIG. 2 is a vertical sectional view of the telescopic shaft for thevehicle steering according to a first embodiment of the presentinvention;

FIG. 3 is a cross sectional view taken along the line X-X in FIG. 2.

FIG. 4A is a perspective view of a plate spring according to the firstembodiment; FIG. 4B is a perspective view of the plate spring accordingto a first modified example of the first embodiment; FIG. 4C is aperspective view of the plate spring according to a second modifiedexample of the first embodiment;

FIG. 5 is a cross sectional view taken along the line X-X in FIG. 2,showing the telescopic shaft for the vehicle steering according to asecond embodiment of the present invention;

FIG. 6A is a perspective view of the plate spring according to thesecond embodiment; FIG. 6B is a perspective view of the plate springaccording to a first modified example of the second embodiment; FIG. 6Cis a perspective view of the plate spring according to a second modifiedexample of the second embodiment;

FIG. 7 is a cross sectional view taken along the line X-X in FIG. 2,showing the telescopic shaft for the vehicle steering according to athird embodiment of the present invention;

FIG. 8A is a perspective view of the plate spring according to the thirdembodiment; FIG. 8B is a perspective view of the plate spring accordingto a first modified example of the third embodiment; FIG. 8C is aperspective view of the plate spring according to a second modifiedexample of the third embodiment;

FIG. 9 is a cross sectional view taken along the line X-X in FIG. 2,showing the telescopic shaft for the vehicle steering according to afourth embodiment of the present invention; and

FIG. 10A is a perspective view of the plate spring according to thefourth embodiment; FIG. 10B is a perspective view of the plate springaccording to a first modified example of the fourth embodiment; FIG. 10Cis a perspective view of the plate spring according to a second modifiedexample of the fourth embodiment.

EMBODIMENTS OF THE INVENTION

A telescopic (extensible/retractable) shaft for a vehicle steeringaccording to embodiments of the present invention will hereinafter bedescribed with reference to the drawings.

(Whole Construction of Steering Shaft for Vehicle)

FIG. 1 is a side view of a steering mechanism unit of an automobile, towhich the telescopic shaft for the vehicle steering according to theembodiment of the present invention is applied.

Referring to FIG. 1, the steering mechanism unit is constructed of anupper steering shaft portion 120 fitted via an upper bracket 101 and alower bracket 102 to a vehicle body sided member 100 and including asteering column 103 and a steering shaft 104 rotatably held in thesteering column 103, a steering wheel 105 fitted to an upper side end ofthe steering shaft 104, a lower steering shaft portion 107 connected viaa universal joint 106 to a lower side end of the steering shaft 104, apinion shaft 109 connected via a steering shaft coupling 108 to thelower steering shaft portion 107, a steering rack shaft 112 connected tothe pinion shaft 109, and a steering rack support member 113 fixed viaan elastic body 111 to another frame 110 of the vehicle body in a waythat supports the steering rack shaft 112.

Herein, the upper steering shaft portion 120 and the lower steeringshaft portion 107 involve using the telescopic shaft for the vehiclesteering (which will hereinafter simply be termed the telescopic shaft)according to the embodiment of the present invention. The lower steeringshaft portion 107 is constructed by fitting a male shaft to a femaleshaft, and this type of lower steering shaft portion 107 is requested tohave performance of absorbing displacement in an axial direction thatoccurs when the automobile travels and of not transmitting thedisplacement and vibrations onto the steering wheel 105. This type ofperformance is requested in the case of taking such a structure that thevehicle body adopts a sub-frame structure, wherein a member 100 forfixing an upper portion of the steering mechanism is separate from aframe 110 to which the steering rack support member 113 is fixed, andthe steering rack support member 113 is fixedly fastened to the frame110 via the elastic body 111 such as a rubber. Further, another case isthat an operator, when fastening the steering shaft coupling 108 to thepinion shaft 109, temporarily contracts the telescopic shaft and fitsand fastens the coupling 108 to the pinion shaft 109, and therefore atelescopic (extensible/retractable) function is needed. Moreover, theupper steering shaft portion 120 provided on the upper portion of thesteering mechanism is constructed by fitting a male shaft to the femaleshaft. This type of upper steering shaft portion 120 is, however,required to have a function of shifting a position of the steering wheel105 in the axial direction in order to obtain a position optimal for adriver to drive the car and adjusting this position, and is thereforerequested to have a function of extending and retracting in the axialdirection. In all the cases described above, what is requested of thetelescopic shaft is to reduce backlash noises at the fitting portion, afeeling of backlash on the steering wheel 105 and slide resistancecaused when sliding in the axial direction.

First Embodiment

FIG. 2 is a vertical sectional view of the telescopic shaft for thevehicle steering according to a first embodiment of the presentinvention.

FIG. 3 is a cross sectional view taken along the line X-X in FIG. 2.

FIG. 4A is a perspective view of a plate spring according to the firstembodiment. FIG. 4B is a perspective view of the plate spring accordingto a first modified example of the first embodiment. FIG. 4C is aperspective view of the plate spring according to a second modifiedexample of the first embodiment.

As shown in FIG. 2, the telescopic shaft for the vehicle steering (whichwill hereinafter be simply referred to as the telescopic shaft) isconstructed of a male shaft 1 and a female shaft 2 that are so fitted toeach other as to be unable to rotate but to be slidable.

As shown in FIG. 3, three lines of axis-directional grooves 3 disposedequally at an interval (phase) of 120 degrees in a peripheral direction,are formed in a way that extends along an outer peripheral surface ofthe male shaft 1. Corresponding to these grooves, three lines ofaxis-directional grooves 5 disposed equally at an interval (phase) of120 degrees in the peripheral direction, are also formed in a way thatextends along an inner peripheral surface of the female shaft 2.

Between the axis-directional grooves 3 of the male shaft 1 and theaxis-directional grooves 5 of the female shaft 2, plural rolling membersor balls defined as rigid spherical members 7 rolling when relativelymoving in the axis-directions of the two shafts 1, 2 are interposed tobe able to roll. The axis-directional groove 5 of the female shaft 2takes a circular-arc shape or Gothic arch shape in section.

The axis-directional groove 3 of the male shaft 1 is configured by apair of flat side surfaces 3 a showing line symmetry with respect to thediameter and inclined, and by a bottom surface 3 b formed flat betweenthe pair of flat side surfaces 3 a.

A plate spring 9 abutting on the spherical member 7 and thus giving apreload thereto is interposed between the axis-directional groove 3 ofthe male shaft 1 and the spherical member 7.

This plate spring 9 integrally has spherical member sided contactportions 9 a abutting at two points on the spherical member 7, groovesurface sided contact portions 9 b spaced away at a predeterminedinterval substantially in the peripheral direction from the respectivespherical member sided contact portions 9 a and abutting on therespective flat side surfaces 3 a of the axis-directional groove 3 ofthe male shaft 1, biasing portions 9 c each connecting the sphericalmember sided contact portion 9 a and the groove surface sided contactportion 9 b on the side of an outer diameter and elastically biasing thespherical member sided contact portion 9 a and the groove surface sidedcontact portion 9 b in a direction of separating the portions 9 a, 9 baway from each other, and a bottom portion 9 d taking a face-to-facerelationship with the bottom surface 3 b of the axis-directional groove3 on the side of an inner diameter.

This biasing portion 9 c takes substantially a U-shape, wherein itsbottom portion is bent substantially in a circular arc shape. Thisbiasing portion 9 c taking the bent shape can elastically bias thespherical member sided contact portion 9 a and the groove surface sidedcontact portion 9 b so as to be separated away from each other.

Thus, according to the first embodiment, the plate spring 9 integrallyhas the contact portions 9 a abutting on the spherical member 7 and thebiasing portions 9 c generating the preload, and hence it is essentialto control the preload so as not to increase too much a contact surfacepressure of the contact portion 9 a upon the spherical member 7.Therefore, according to the first embodiment, the plate spring 9 is setto have such a structure that the preload (i.e., a load generated by thebiasing portion 9 c when relatively rotating the male shaft 1 aroundinside the female shaft 2) generated by the biasing portion 9 c does notexceed an allowable value of the surface pressure caused by the contactportion 9 a upon the spherical member 7.

As illustrated in FIG. 3, three lines of axis-directional grooves 4disposed equally at an interval (phase) of 120 degrees in the peripheraldirection, are formed in a way that extends on the outer peripheralsurface of the male shaft 1. Corresponding to these grooves, three linesof axis-directional grooves 6 disposed equally at an interval (phase) of120 degrees in the peripheral direction, are also formed in a way thatextends on the inner peripheral surface of the female shaft 2.

Between the axis-directional grooves 4 of the male shaft 1 and theaxis-directional grooves 6 of the female shaft 2 corresponding thereto,plural pieces of cylindrical rigid members 8 (which are also termedslide members or needle rollers in the present specification) slidingwhen the two shafts 1, 2 move relatively in the axis-direction, areinterposed with a minute gap. These axis-directional grooves 4, 6 eachtakes a circular-arc shape or Gothic arch shape in section.

As shown in FIG. 2, an end portion of the male shaft 1 is formed with asmall-diameter portion 1 a. This small-diameter portion 1 a is providedwith a stopper plate 10 regulating an axis-directional movement of theneedle roller 8. This stopper plate 10 is constructed of anaxis-directional preloading elastic member 11 consisting of a Bellevillespring and a pair of flat plates 12, 13 for holding the axis-directionalpreloading elastic member 11 therebetween.

In the first embodiment, the stopper plate 10 is firmly fixed byplastically deforming by clinching or caulking to the small-diameterportion 1 a in a way that fits the flat plate 13, the axis-directionalpreloading elastic member 11 and the flat plate 12 in this sequence tothe small-diameter portion 1 a. In this way, the stopper plate 10 isfixed in the axis-direction. It should be noted that a fixing method ofthe stopper plate 10 is not limited to plastically deforming byclinching or caulking and may involve employing means such as a stopperring, a screwing means and a push nut. Further, the stopper plate 10 isso constructed as to be capable of preloading the needle roller 8 not tomove in the axis-direction by the axis-directional preloading elasticmember 11 (Belleville spring) in a way that butting the flat plate 13against the needle roller 8.

Further, according to the first embodiment, six pieces of protrudedportions 14 each taking substantially a circular arc shape and formedcoaxially in the axis-direction with the six lines of axis-directionalgrooves 3, 4 on the outer peripheral surface of the male shaft 1, arefitted with gaps in the radial direction into the six lines ofaxis-directional grooves 5, 6 of the female shaft 2.

Accordingly, if the spherical member 7 or the cylindrical member 8 comesoff the male shaft 1 or is damaged due to any cause, the protrudedportions 14 of the male shaft 1 fit into the axis-directional grooves 5,6 of the female shaft 2, whereby the male shaft 1 and the female shaft 2can transfer torque and can perform a role of a fail-safe function.

Further, on this occasion, since the gaps are provided between theaxis-directional grooves 5, 6 and the protruded portions 14, the drivercan feel the great backlash through on the steering wheel, and canpercept a fault etc in the steering system.

Moreover, the protruded portions 14 are aligned in the axis-directionwith the spherical members 7 and the cylindrical members 8 and thereforeperform a role as the stopper for regulating the axis-directionalmovements of the spherical members 7 and the cylindrical members 8,thereby reducing a possibility that the spherical members 7 and thecylindrical members 8 might come off and enabling the fail-safe functionto be further improved.

Furthermore, the protruded portions 14 are aligned in the axis-directionwith the spherical members 7 and the cylindrical members 8, and it istherefore feasible to attain a compact configuration by reducingdiameter-directional dimensions of the male shaft 1 and the female shaft2.

Moreover, a lubricating agent may be applied over between theaxis-directional groove 3 of the male shaft 1, the axis-directionalgroove 5 of the female shaft 2, the plate spring 9 and the sphericalmember 7. Further, the lubricating agent may also be applied overbetween the axis-directional groove 4 of the male shaft 1, andcylindrical member 8 and the axis-directional groove 6 of the femaleshaft 2.

In the thus-constructed telescopic shaft, the spherical members 7 areinterposed between the male shaft 1 and the female shaft 2, and theplate spring 9 preloads the spherical member 7 against the female shaft2 to such an extent as not to cause the backlash. It is thereforepossible to, when not transferring the torque, surely prevent thebacklash between the male shaft 1 and the female shaft 2, and the maleshaft 1 and the female shaft 2, when making the relative movements inthe axis-direction, can slide with a slide load stably without causingany backlash.

When transferring the torque, the plate springs 9 elastically deform andrestrict the spherical members 7 in the peripheral direction, and thethree lines of cylindrical members 8 interposed between the male shaft 1and the female shaft 2 perform the principal role of transferring thetorque.

For instance, when the torque is inputted from the male shaft 1, at aninitial stage, there is no backlash because of being preloaded by theplate springs 9, and the plate springs 9 generate reaction against thetorque, thus transferring the torque. The whole torques are transferredin a state where the transmission torque between the male shaft 1, theplate springs 9, the spherical members 7 and the female shaft 2 isequilibrated with an input torque.

When the torque further increases, gaps in a rotating direction betweenthe male shaft 1 and the female shaft 2 via the cylindrical members 8disappear, and the increased amount of torque is thereafter transferredby the cylindrical members 8 through the male shaft 1 and the femaleshaft 2. Hence, it is feasible to surely prevent the backlash in therotating direction between the male shaft 1 and the female shaft 2 andto transfer the torque in the state exhibiting the high rigidity.

From the construction explained so far, according to the firstembodiment, the cylindrical members 8 are provided other than thespherical members 7, and therefore, when inputting the great torque, alarge proportion of the load quantity can be sustained by thecylindrical members 8. Accordingly, durability can be improved bydecreasing the contact pressure between the axis-directional grooves 5of the female shaft 2 and the spherical members 7, and, when with thelarge torque-load, the torque can be transferred in the high-rigiditystate.

Further, as the cylindrical members 8 abut on the male shaft 1 and thefemale shaft 2, the torsional torque upon the spherical members 7 isreduced, a lateral slide of the plate springs 9 is restrained, and, as aresult, an excess of hysteresis can be restrained.

Thus, according to the first embodiment, the stable slide load can beactualized, and the torque can be transferred in the high-rigidity stateby surely preventing the backlash in the rotating direction.

It is to be noted that the spherical members 7 be preferably rigidballs. It is also preferable that the rigid cylindrical members 8 beneedle rollers.

The cylindrical member 8 (which will hereinafter be referred to as theneedle roller) 8 receives the load in line contact, and therefore has avariety of effects such as restraining the contact pressure lower thanby the ball receiving the load in point contact. Accordingly, thefollowing items are superior to the case of taking an all-line ballrolling structure.

An attenuation effect at the slide portion is greater than in the ballrolling structure. Hence, vibration absorbing performance is high.

The needle roller 8 is brought into micro-contact with the male shaftand the female shaft, and hence an amplitude of a slide load fluctuationcan be restrained low, whereby vibrations due to this fluctuation arenot transferred up to the steering.

If the same amount of torque is transferred, the contact pressure can berestrained lower by the needle roller, and therefore the space can beutilized effectively by enabling the length in the axis-direction to beshortened.

If the same amount of torque is transferred, the contact pressure can berestrained lower by the needle roller, and hence there is no necessityfor an additional process for hardening the surface of theaxis-directional groove of the female shaft by thermal treatment etc.

The number of components can be decreased.

An assembling property can be enhanced.

An assembly cost can be restrained.

As described above, the needle roller performs the key role fortransferring the torque to between the male shaft 1 and the female shaft2, and gets the slide-contact with the inner peripheral surface of thefemale shaft 2. The following are excellent points of the needle rolleras compared with the conventional spline-fitting.

The needle roller is a product of mass-production and is thereforeextremely low of cost.

The needle roller is polished after the thermal treatment and istherefore high of surface hardness and is excellent of resistance ofabrasion.

The needle roller has been polished and is therefore fine of surfaceroughness and is low of a coefficient of friction at the sliding time,thereby enabling the slide load to be restrained low.

A length and layout of the needle roller can be changed depending on ausage condition, and consequently the needle roller is flexible to avariety of applications without changing the design concept.

A case where the coefficient of friction at the sliding time must befurther decreased, might arise depending the usage condition. At thistime, the slide characteristic can be changed simply by executing thesurface treatment upon only the needle roller, and hence the needleroller is flexible to the variety of applications without changing thedesign concept.

The needle rollers each having a different outer diameter can bemanufactured on the unit of several microns at a low cost, whereby gapsbetween the male shaft and the needle roller and between the needleroller and the female shaft can be minimized by selecting the diameterof the needle roller. Hence, the rigidity of the shaft in the torsionaldirection can be easily improved.

Further, the plate springs 9 each includes, on the right and left sides,respectively, the pair of spherical member sided contact portions 9 aabutting at the two points on the spherical members 7, the pair ofgroove surface sided contact portions 9 b spaced away at thepredetermined interval substantially in the peripheral direction fromthe spherical member sided contact portions 9 a and abutting on the flatside surfaces 3 a of the axis-directional groove 3 of the male shaft 1,the pair of biasing portions 9 c biasing elastically the sphericalmember sided contact portions 9 a and the groove surface sided contactportions 9 b in the direction of separating the portions 9 a, 9 b fromeach other, and the pair of bottom portions 9 d in the face-to-facerelationship with the bottom surface 3 b of the axis-directional groove3.

This biasing portion 9 c takes substantially the U-shape, wherein itsbottom portion is bent substantially in the circular arc shape. Thisbiasing portion 9 c taking the bent shape can elastically bias thespherical member sided contact portion 9 a and the groove surface sidedcontact portion 9 b so as to be separated away from each other.Accordingly, the plate spring 9, with its spherical member sided contactportion 9 a being able to become flexural sufficiently through thebiasing portion 9 b, can ensure a sufficient amount of flexure.

Now, according to the first embodiment, as shown in FIGS. 3 and 4A, thespherical member sided contact portions 9 a of the plate spring abuttingon the spherical member 7 have the high surface hardness (desirablyequal to or higher than HRC40), and other portions (i.e., the groovesurface sided contact portions 9 b, the biasing portion 9 c and thebottom portion 9 d) are set low of their surface hardness (desirablyequal to or lower than HRC30). Note that the spherical member sidedcontact portions 9 a having the high surface hardness are, in FIG. 4A, apair of flat and rectangular portions extending in the axis-directionand exhibiting, as a matter of course, the bilateral symmetry.

With this configuration, the spherical member sided contact portions 9 aabutting on the spherical member 7 are rigid and are therefore capableof sufficiently bearing the stress occurred at the contact points withthe spherical member 7.

By contrast, the portions exhibiting the low surface hardness are easyto become flexural when receiving the displacement, thereby making itpossible to prevent occurrence of an excessive stress at the contactpoints with the spherical member 7.

Namely, providing the difference in degree of hardness (rigidity) aimsat taking a balance between the surface pressure (stress) at the contactpoints and the preload occurred at the biasing portions 9 c. If usingthe conventional integral molding product and the plate spring havingthe uniform plate thickness, the balance therebetween is extremely hardto take. It should be noted that the embodiment, which will hereinafterbe exemplified, is a structure invented entirely for taking thisbalance.

In the first embodiment, for thus taking the preload balance of theplate spring 9, the rigidity of the spherical member sided contactportions 9 a of the plate spring 9 is set higher than the rigidity ofthe groove surface sided contact portions 9 b.

From what has been discussed above, according to the first embodiment,the plate spring 9 is provided with the space between the sphericalmember sided contact portion 9 a abutting on the spherical member 7 andthe groove surface sided contact portion 9 b abutting on theaxis-directional groove 3, and the elastic connection is establishedtherebetween. With this contrivance, when setting, the stress occurredat the contact portion of the plate spring 9 with the spherical member 7can be reduced, and the desired preload performance can be acquired overa long period of time by preventing a permanent strain of the platespring 9 due to permanent deformation.

Furthermore, the plate spring 9 is capable of ensuring the sufficientamount of flexure, and the excessive load (stress) is applied to neitherthe spherical member 7 nor the plate spring 9, and hence, whentransferring the torque, it is feasible to decrease the stress occurredat the contact point between the spherical member 7 and the plate spring9, whereby the preload performance can be maintained by preventing the[permanent strain] due to the permanent deformation without causing thehigh stress.

Moreover, owing to the contact points with the spherical member 7,firmly, the portions exhibiting the spring property are set easy to getflexural, thus making it compatible for the single member to have therace surfaces and the spring property. Further, the structure in thefirst embodiment is that the cylindrical members 8 mainly transfer thetorque, and therefore a further excessive stress is not occurred amongthe male shaft 1, the female shaft 2, the plate springs 9 and thespherical members 7.

Accordingly, the permanent strain of the plate spring 9 is prevented byhindering the occurrence of the excessive stress on the plate spring 9,thereby enabling the desired preload performance to be maintained overthe long period of time. In addition, the dimensional accuracy is notrequired to be strictly managed, and the plate spring 9 and the raceportion can be made from the single material, thereby making it feasibleto reduce the manufacturing cost in a way that facilitates theassembling.

Next, FIG. 4B is a perspective view of the plate spring 9 according to afirst modified example of the first embodiment.

According to the first modified example, the biasing portions 9 cdefined as the curled portions of the plate spring 9 each is formed witha plurality of holes 21, aligned in the axis-direction, for decreasingthe biasing force, thus making it easy for the plate spring 9 to becomeflexural.

With this arrangement, none of the excessive stress is applied to thecontact points with the spherical member 7. Namely, when the torque loadis applied, the spherical member 7 relatively moves in the rotatingdirection, however, at this time, the biasing portion 9 c as the curledportion is set easy to become flexural, so that the excessive stress isnot applied to the contact point with the spherical member 7. Note thatthe surface hardness may be, even when uniform on the whole, partiallychanged as in the first embodiment.

Next, FIG. 4C is a perspective view of the plate spring according to asecond modified example of the first embodiment.

A bent R-portion at the root of the plate spring 9, which is formedbetween the spherical member sided contact portion 9 a and the bottomsurface 9 d, is formed with a plurality of holes 22, aligned in theaxis-direction, for decreasing the biasing force, thereby making it easyfor the plate spring 9 to get flexural.

With this contrivance, none of the excessive stress is applied to thecontact points with the spherical member 7. Namely, before the torqueload is applied (at which time the stress occurs at the contact pointsof the plate spring 9 due to the preload generated by assembling), asthe portion formed with the hole 22 in the bent R-portion of the platespring 9 is easy to become flexural, none of the excessive stress isapplied to the contact points of the plate spring 9 with the sphericalmember 7 when assembled. Note that the surface hardness may be, evenwhen uniform on the whole, partially changed as in the first embodiment.

Second Embodiment

FIG. 5 is a cross sectional view taken along the line X-X in FIG. 2,showing the telescopic shaft for the vehicle steering according to asecond embodiment of the present invention.

FIG. 6A is a perspective view of the plate spring according to thesecond embodiment. FIG. 6B is a perspective view of the plate springaccording to a first modified example of the second embodiment. FIG. 6Cis a perspective view of the plate spring according to a second modifiedexample of the second embodiment.

As shown in FIGS. 5 and 6A, according to the second embodiment, ascompared with the first embodiment, the plate thickness of the sphericalmember sided contact portion 9 a abutting on the spherical member 7 isset thicker than a plate thickness of a portion extending from thegroove surface sided contact portion 9 b to the biasing portion 9 c.Thus, according to the second embodiment, the preload balance describedabove is taken in a way that differentiates the rigidities of thespherical member sided contact portions 9 a and the groove surface sidedcontact portions 9 b of the plate spring 9 from each other by giving adifference in the plate thicknesses between these two portions 9 a and 9b. Note that the surface hardness may be, even when uniform on thewhole, partially changed as in the first embodiment.

From what has been discussed above, according to the second embodiment,the plate springs 9 are capable of ensuring the sufficient amount offlexure, with the excessive load (stress) being applied to neither thespherical members 7 nor the plate springs 9, and, when transferring thetorque, the stress occurred at the contact portion between the sphericalmembers 7 and the plate springs 9 can be reduced. With this contrivance,the high stress does not occur, and the preload performance can bemaintained over a long period of time by preventing the [permanentstrain] due to the permanent deformation.

Moreover, owing to the contact points with the spherical members 7,firmly, the portions exhibiting the spring property are set easy to getflexural, thus making it compatible for the single member to have therace surface and the spring property.

Accordingly, the permanent strain of the plate spring 9 is prevented byhindering the occurrence of the excessive stress on the plate spring 9,thereby enabling the desired preload performance to be maintained overthe long period of time. In addition, the dimensional accuracy is notrequired to be strictly managed, and the plate spring 9 and the raceportion can be made from the single material, thereby making it feasibleto reduce the manufacturing cost in a way that facilitates theassembling.

Next, FIG. 6B is a perspective view of the plate spring according to afirst modified example of the second embodiment. According to the firstmodified example, the curled portions as the biasing portions 9 c of theplate spring 9 each is formed with a plurality of holes 21, aligned inthe axis-direction, for decreasing the biasing force, thus making iteasy for the plate spring 9 to become flexural. With this arrangement,none of the excessive stress is applied to the contact point with thespherical member 7. Namely, when the torque load is applied, thespherical members 7 relatively move in the rotating direction, however,at this time, the biasing portions 9 c (the curled portions) are seteasy to become flexural, so that the excessive stress is not applied tothe contact points with the spherical members 7. Note that the surfacehardness may be, even when uniform on the whole, partially changed as inthe first embodiment.

Next, FIG. 6C is a perspective view of the plate spring according to asecond modified example of the second embodiment. A bent R-portion atthe root of the plate spring 9, which is formed between the sphericalmember sided contact portion 9 a and the bottom surface 9 d, is formedwith a plurality of holes 22, aligned in the axis-direction, fordecreasing the biasing force, thereby making it easy for the platespring 9 to get flexural. With this contrivance, none of the excessivestress is applied to the contact points with the spherical member 7.Namely, before the torque load is applied (at which time the stressoccurs at the contact point of the plate spring 9 due to the preloadgenerated by assembling), as the portion formed with the hole 22 in thebent R-portion of the plate spring 9 is easy to become flexural, none ofthe excessive stress is applied to the contact points of the platespring 9 with the spherical member 7 when assembled. Note that thesurface hardness may be, even when uniform on the whole, partiallychanged as in the first embodiment.

Third Embodiment

FIG. 7 is a cross sectional view taken along the line X-X in FIG. 2,showing the telescopic shaft for the vehicle steering according to athird embodiment of the present invention.

FIG. 8A is a perspective view of the plate spring according to the thirdembodiment. FIG. 8B is a perspective view of the plate spring accordingto a first modified example of the third embodiment. FIG. 8C is aperspective view of the plate spring according to a second modifiedexample of the third embodiment.

As illustrated in FIGS. 7 and 8, according to the third embodiment, ascompared with the first embodiment, the spherical member sided contactportions 9 a abutting on the spherical member 7 each is formedsubstantially in the circular arc shape. With this configuration, thecontact surface pressure can be made lower than in the plane shape.According to the third embodiment, the spherical member sided contactportions 9 a abutting on the spherical member 7 each is formedsubstantially in the circular arc shape and is therefore set higher thanthe groove surface sided contact portion 9 b taking substantially theplane shape. Note that the surface hardness may be, even when uniform onthe whole, partially changed as in the first embodiment.

From what has been discussed above, according to the third embodiment,the plate spring 9 is capable of ensuring the sufficient amount offlexure, with the excessive load (stress) being applied to neither thespherical member 7 nor the plate spring 9, and, when transferring thetorque, the stress occurred at the contact portions between thespherical member 7 and the plate spring 9 can be reduced. With thiscontrivance, the high stress does not occur, and the preload performancecan be maintained over a long period of time by preventing the[permanent strain] due to the permanent deformation.

Moreover, the contact points with the spherical member 7, the portionsexhibiting the spring property firmly are set easy to get flexural, thusmaking it compatible for the single member to have the race surface andthe spring property.

Accordingly, the permanent strain of the plate spring 9 is prevented byhindering the occurrence of the excessive stress on the plate spring 9,thereby enabling the desired preload performance to be maintained overthe long period of time. In addition, the dimensional accuracy is notrequired to be strictly managed, and the plate spring 9 and the raceportion can be made from the single material, thereby making it feasibleto reduce the manufacturing cost in a way that facilitates theassembling.

Next, FIG. 8B is a perspective view of the plate spring according to afirst modified example of the third embodiment. According to the firstmodified example, the curled portion as the biasing portion 9 c of theplate spring 9 is formed with a plurality of holes 21, aligned in theaxis-direction, for decreasing the biasing force, thus making it easyfor the plate spring 9 to become flexural. With this arrangement, noneof the excessive stress is applied to the contact point with thespherical member 7. Namely, when the torque load is applied, thespherical member 7 relatively moves in the rotating direction, however,at this time, the biasing portion 9 c (the curled portion) is set easyto become flexural, so that the excessive stress is not applied to thecontact point with the spherical member 7. Note that the surfacehardness may be, even when uniform on the whole, partially changed as inthe first embodiment.

Next, FIG. 8C is a perspective view of the plate spring according to asecond modified example of the third embodiment. A bent R-portion at theroot of the plate spring 9, which is formed between the spherical membersided contact portion 9 a and the bottom surface 9 d, is formed with aplurality of holes 22, aligned in the axis-direction, for decreasing thebiasing force, thereby making it easy for the plate spring 9 to getflexural. With this contrivance, none of the excessive stress is appliedto the contact points with the spherical member 7. Namely, before thetorque load is applied (at which time the stress occurs at the contactpoints of the plate spring 9 due to the preload generated byassembling), as the portion formed with the hole 22 in the bentR-portion of the plate spring 9 is easy to become flexural, none of theexcessive stress is applied to the contact points of the plate spring 9with the spherical member 7 when assembled. Note that the surfacehardness may be, even when uniform on the whole, partially changed as inthe first embodiment.

Fourth Embodiment

FIG. 9 is a cross sectional view taken along the line X-X in FIG. 2,showing the telescopic shaft for the vehicle steering according to afourth embodiment of the present invention.

FIG. 10A is a perspective view of the plate spring according to thefourth embodiment. FIG. 10B is a perspective view of the plate springaccording to a first modified example of the fourth embodiment. FIG. 10Cis a perspective view of the plate spring according to a second modifiedexample of the fourth embodiment.

As shown in FIGS. 9 and 10A, according to the fourth embodiment, ascompared with the first embodiment, the plate thickness of the sphericalmember sided contact portion 9 a abutting on the spherical member 7 isset thicker than a plate thickness of a portion extending from thegroove surface sided contact portion 9 b to the biasing portion 9 c, andthe surface abutting on the spherical member 7 is formed substantiallyin the circular arc shape. With this arrangement, the contact surfacepressure with the spherical member 7 can be made lower than in the planeshape. Note that the surface hardness may be, even when uniform on thewhole, partially changed as in the first embodiment.

From what has been discussed above, according to the fourth embodiment,the plate spring 9 is capable of ensuring the sufficient amount offlexure, with the excessive load (stress) being applied to neither thespherical member 7 nor the plate spring 9, and, when transferring thetorque, the stress occurred at the contact portion between the sphericalmember 7 and the plate spring 9 can be reduced. With this contrivance,the high stress does not occur, and the preload performance can bemaintained over a long period of time by preventing the [permanentstrain] due to the permanent deformation.

Moreover, the contact points with the spherical member 7, that is, theportions exhibiting the spring property firmly are set easy to getflexural, thus making it compatible for the single member to have therace surface and the spring property.

Accordingly, the permanent strain of the plate spring 9 is prevented byhindering the occurrence of the excessive stress on the plate spring 9,thereby enabling the desired preload performance to be maintained overthe long period of time. In addition, the dimensional accuracy is notrequired to be strictly managed, and the plate spring 9 and the raceportion can be made from the single material, thereby making it feasibleto reduce the manufacturing cost in a way that facilitates theassembling.

Next, FIG. 10B is a perspective view of the plate spring according to afirst modified example of the fourth embodiment. According to the firstmodified example, the curled portions as the biasing portions 9 c of theplate spring 9 each is formed with a plurality of holes 21, aligned inthe axis-direction, for decreasing the biasing force, thus making iteasy for the plate springs 9 to become flexural. With this arrangement,none of the excessive stress is applied to the contact points with thespherical member 7. Namely, when the torque load is applied, thespherical members 7 relatively move in the rotating direction, however,at this time, the biasing portions 9 c are set easy to become flexural,so that the excessive stress is not applied to the contact point withthe spherical member 7. Note that the surface hardness may be, even whenuniform on the whole, partially changed as in the first embodiment.

Next, FIG. 10C is a perspective view of the plate spring according to asecond modified example of the fourth embodiment. A bent R-portion atthe root of the plate spring 9, which is formed between the sphericalmember sided contact portion 9 a and the bottom surface 9 d, is formedwith a plurality of holes 22, aligned in the axis-direction, fordecreasing the biasing force, thereby making it easy for the platespring 9 to get flexural. With this contrivance, none of the excessivestress is applied to the contact points with the spherical member 7.Namely, before the torque load is applied (at which time the stressoccurs at the contact points of the plate spring 9 due to the preloadgenerated by assembling), as the portion formed with the hole 22 in thebent R-portion of the plate spring 9 is easy to become flexural, none ofthe excessive stress is applied to the contact points of the platespring 9 with the spherical member 7 when assembled. Note that thesurface hardness may be, even when uniform on the whole, partiallychanged as in the first embodiment.

It should be noted that the present invention is not limited to theembodiments discussed above and can be modified in a variety of forms.

As explained above, the elastic members each is provided with the spacebetween the transferring member sided contact portion abutting on thefirst torque transferring member and the groove surface sided contactportion abutting on the axis-directional groove, and the elasticconnection is established therebetween. With this contrivance, whensetting, the stress occurred at the contact portion between the firsttorque transferring member and the elastic member can be reduced, andthe desired preload performance can be acquired over the long period oftime by preventing the permanent strain of the elastic member due to thepermanent deformation.

Furthermore, the elastic member is capable of ensuring the sufficientamount of flexure, and the excessive load (stress) is applied to neitherthe first torque transferring member nor the elastic member, and hence,when transferring the torque, it is feasible to decrease the stressoccurred at the contact point between the first torque transferringmember and the elastic member, whereby the preload performance can bemaintained over the long period of time by preventing the [permanentstrain] due to the permanent deformation without causing the high stresswithout causing high stress.

Moreover, the contact point with the spherical member 7, the portionexhibiting the spring property firmly, is set easy to get flexural, thusmaking it compatible for the single member to have the race surface andthe spring property. Further, the structure in the fourth embodiment isthat the second torque transferring member mainly transfers the torque,and therefore a further excessive stress is not occurred among the maleshaft, the female shaft, the elastic members and the first torquetransferring members.

Accordingly, the permanent strain of the elastic member is prevented byhindering the occurrence of the excessive stress on the elastic members,thereby enabling the desired preload performance to be maintained overthe long period of time. In addition, the dimensional accuracy is notrequired to be strictly managed, and the elastic members and the raceportions can be made from the single material, thereby making itfeasible to reduce the manufacturing cost in a way that facilitates theassembling.

1. A telescopic shaft for a vehicle steering, assembled in a steeringshaft of a vehicle and constructed by fitting a male shaft and a femaleshaft to each other so as to be unable to rotate but to be slidable,said telescopic shaft comprising: a first torque transferring memberinterposed via an elastic member between one line of axis-directionalgroove and one line of axis-directional groove formed respectively on anouter peripheral surface of said male shaft and on an inner peripheralsurface of said female shaft; and a second torque transferring memberinterposed between another line of axis-directional groove and anotherline of axis-directional groove formed respectively on the outerperipheral surface of said male shaft and on the inner peripheralsurface of said female shaft, said elastic member including: atransferring member sided contact portion abutting on said first torquetransferring member; a groove sided contact portion spaced away at anpredetermined interval substantially in a peripheral direction from saidtransferring member sided contact portion and abutting on a groovesurface of the axis-directional groove of said male shaft or said femaleshaft; and a biasing portion elastically biasing said transferringmember sided contact portion and said groove sided contact portion insuch a direction as to separate from each other, wherein a rigidity ofsaid transferring member sided contact portion is differentiated from arigidity of said groove sided contact portion.
 2. A telescopic shaft fora vehicle steering according to claim 1, wherein said first torquetransferring member is a rolling member rolling when both of said maleshaft and said female shaft make relative movements in theaxis-direction, and said second torque transferring member is a slidemember sliding when both of said male shaft and said female shaft makethe relative movements in the axis-direction.
 3. A telescopic shaft fora vehicle steering according to claim 1, wherein said biasing portion ofsaid elastic member takes a bent shape bent between said transferringmember sided contact portion and said groove surface sided contactportion.
 4. A telescopic shaft for a vehicle steering according to claim1, wherein said elastic member is constructed of an integral moldingproduct made from thin plate spring steel.
 5. A telescopic shaft for avehicle steering according to claim 1, wherein surface hardness of saidtransferring member sided contact portion is set higher than surfacehardness of a portion extending from said groove surface sided contactportion to said biasing portion.
 6. A telescopic shaft for a vehiclesteering according to claim 1, wherein said biasing portion is formedwith holes for reducing a biasing force.
 7. A telescopic shaft for avehicle steering according to claim 1, wherein a plate thickness of saidtransferring member sided contact portion is set thicker than a platethickness of a portion extending from said groove surface sided contactportion to said biasing portion.
 8. A telescopic shaft for a vehiclesteering according to claim 1, wherein said transferring member sidedcontact portion is formed substantially in a circular arch shape.
 9. Atelescopic shaft for a vehicle steering, comprising: a male shaft formedwith first and second axis-directional grooves extending in anaxis-direction on an outer peripheral surface at an interval of apredetermined angle; a female shaft disposed coaxially with said maleshaft, formed with third and fourth axis-directional grooves extendingin the axis-direction on an inner peripheral surface in a way thatcorresponds to said first and second axis-direction grooves, and fittedonto said male shaft; a first torque transferring member interposedbetween said first axis-directional groove of said male shaft and saidthird axis-directional groove of said female shaft; an elastic memberinterposed between said first torque transferring member and said firstaxis-directional groove of said male shaft, and extending in theaxis-direction; a second torque transferring member interposed betweensaid second axis-directional groove of said male shaft and said fourthaxis-directional groove of said female shaft; and said telescopic shaftbeing assembled in a steering shaft of a vehicle and constructed byfitting said male shaft and said female shaft to each other so as to beunable to relatively rotate but to be slidable, wherein said elasticmember is integrally formed with a first contact portion at which theelastic member is in contact with said first torque transferring member,a second contact portion at which said elastic member is in contact withsaid groove surface of the male shaft, and a biasing portion holdingelastically said members in the preloaded and contacted state with thefirst and the second contacting portions being spaced away from eachother; and the preload caused by said biasing member is so set not toexceed a tolerance value of a surface pressure at said second contactportion against said first torque transferring member.
 10. A telescopicshaft for a vehicle steering according to claim 9, wherein said firstaxis-directional groove of said male shaft has groove sided surfacesexhibiting a line symmetry with respect to a diametrical direction and agroove bottom surface connecting said groove sided surfaces, said firstcontact portion of said elastic member is constructed of transferringmember sided contact portions each abutting on said first transferringmember, said second contact portion of said elastic member isconstructed of groove surface sided contact portions each abutting onsaid groove sided surface, said biasing portion connecting saidtransferring member sided contact portion to said groove surface sidedcontact portion on the side of an outer diameter and biasing said twocontact portions in such a direction as to separate from each other, andsaid elastic member further integrally has a connecting portionconnecting said transferring member sided contact portion to said groovesurface sided contact portion on the side of an inner diameter.
 11. Atelescopic shaft for a vehicle steering according to claim 9, whereinsaid first torque transferring member is constructed of a plurality ofspherical rolling members, and said second torque transferring member isconstructed of a needle roller.
 12. A telescopic shaft for a vehiclesteering according to claim 2, wherein said biasing portion of saidelastic member takes a bent shape bent between said transferring membersided contact portion and said groove surface sided contact portion. 13.A telescopic shaft for a vehicle steering according to claim 2, whereinsaid elastic member is constructed of an integral molding product madefrom thin plate spring steel.
 14. A telescopic shaft for a vehiclesteering according to claim 2, wherein surface hardness of saidtransferring member sided contact portion is set higher than surfacehardness of a portion extending from said groove surface sided contactportion to said biasing portion.
 15. A telescopic shaft for a vehiclesteering according to claim 6, wherein said biasing portion is formedwith holes for reducing a biasing force.
 16. A telescopic shaft for avehicle steering according to claim 2, wherein a plate thickness of saidtransferring member sided contact portion is set thicker than a platethickness of a portion extending from said groove surface sided contactportion to said biasing portion.
 17. A telescopic shaft for a vehiclesteering according to claim 2, wherein said transferring member sidedcontact portion is formed substantially in a circular arch shape.
 18. Atelescopic shaft for a vehicle steering according to claim 10, whereinsaid first torque transferring member is constructed of a plurality ofspherical rolling members, and said second torque transferring member isconstructed of a needle roller.